1. Field of the Invention
The present invention relates to methods of etching a material layer formed on a semiconductor wafer, and more particularly, to a method of etching a material layer formed on a semiconductor wafer using a surface wave coupled plasma etching apparatus.
2. Description of the Related Art
As circular semiconductor wafers increase in size as well as in the level of integration of semiconductor devices, the need for an effective etching apparatus for etching fine patterns has increased. In particular, an etching apparatus capable of forming fame patterns, having accurate critical dimensions and uniformity in size, on a large circular semiconductor wafer is required.
A surface wave coupled plasma etching apparatus has been suggested to satisfy this demand. In the surface wave coupled plasma etching apparatus, surface waves generated by an insulation plate are transmitted through a glass plate to a reaction chamber to excite an etching gas, thereby generating plasma. The produced surface wave plasma acts on a semiconductor wafer to etch a material layer, for example, an oxide layer.
The reaction chamber of a conventional surface wave plasma etching apparatus is heated to a high temperature of 180 C. in order to suppress loss of etching gas. However, since the glass plate that transmits surface waves has low heat transfer efficiency, the temperature of the glass plate usually remains at a low temperature of 120-150 C. when a process is not performed, compared to the reaction chamber made of aluminum. Also, it is easy to heat the glass plate to a high temperature of 250 C. during etching process. Due to the low heat transfer efficiency of the glass plate, the temperature distribution across the glass plate is not even during the etching process, resulting in properties of surface wave coupled plasma that are not uniform.
To avoid these problems, a method of preheating the glass plate has been suggested, in which the glass plate is pre-heated while etching a semiconductor dummy wafer loaded into a reaction chamber using an etching gas, for example, a gas mixture containing C4F8, CO, O2 and Ar. However, such a glass plate pre-heating method takes more than 30 minutes, and fluorine (F) contained in the etching gas mixture causes damage to the glass plate, reducing the life of the apparatus. Also, carbon (C) contained in the etching gas mixture produces a polymer on the glass plate, thereby making transmission of surface wave coupled plasma through the glass plate difficult.
An object of the present invention is to provide a method of etching a material layer formed on a semiconductor wafer, by which, with the use of a surface wave coupled plasma etching apparatus, the preheating time of a glass plate that conducts surface waves can be sharply reduced.
In one embodiment, the present invention provides a method of etching a material formed on a semiconductor wafer. Surface waves are generated by an insulation plate of a plasma etching apparatus. The surface waves are transmitted to a glass plate disposed beneath said insulation plate. A gas having a high ion density, such as argon (Ar) or xenon (Xe), is supplied. The glass plate is preheated by exciting the gas prior to etching the material layer.
Preferably, in the step of preheating the glass plate, a bias power of about 500-2500 watts is applied to a lower electrode on which the semiconductor wafer is loaded, and the generated microwaves have a source power of about 1000-4000 watts through the insulation plate. Also, in the step of supplying a gas, a pressure of about 30-60 mTorr is applied in a process chamber in the plasma etching apparatus. The step of etching the material layer preferably includes supplying an oxygen gas into the process chamber of the plasma etching apparatus. Preferably the glass plate is preheated to about 250-350 C. The material layer is preferably an oxide film.
In another embodiment, there is provided a method of etching a material film formed on a semiconductor wafer, the method comprising loading a semiconductor dummy wafer into a reaction chamber of a surface wave coupled plasma etching apparatus which has an insulation plate which is capable of generating surface waves by microwaves, and a glass plate placed below the insulation plate, for transmitting the produced surface waves. Then, the glass plate is rapidly pre-heated by generating an Ar or Xe surface wave coupled plasma which has a high ion density and a large mass. After exhausting the argon or xenon gas which has been used to generate the surface wave coupled plasma, the semiconductor dummy wafer is unloaded. Then, a semiconductor wafer is loaded into the reaction chamber, and an etching gas is supplied into the reaction chamber into which the semiconductor wafer has been loaded. After generating the surface wave coupled plasma by exciting the etching gas, a material film formed on the semiconductor wafer is etched using the plasma generated from the etching gas by surface waves.
In another embodiment, a method is presented for etching an oxide film formed on a semiconductor wafer loaded onto a reaction chamber of a surface wave coupled plasma etching apparatus having an insulation plate capable of generating surface waves by transmission of microwaves of about 1000-4000 watts, and a glass plate placed below the insulation plate, for transmitting the surface waves. The glass plate is preferably preheated by generating an argon (Ar) or xenon (Xe) surface wave coupled plasma which has a high ion density and a large mass, to about 250-350 C. and applying to a lower electrode on which the semiconductor wafer is loaded, a bias power of about 500-2500 watts. The pressure of the process chamber is preferably about 30-60 mTorr.
In the present invention as described above, a gas such as Ar or Xe is used during the etching process which is performed in a surface wave coupled plasma etching apparatus. Because the gas, that is, Ar or Xe, has a high ion density and a large mass, it can preheat the glass plate that transmits surface waves within a short time.
Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings.